Upper Big Nemaha J-12a Reservoir Report
Last Updated: December 5, 2025
Upper Big Nemaha J-12a is a vital water resource infrastructure located in Johnson, Nebraska, designed by the USDA NRCS and regulated by the NE DNR.
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Summary
Completed in 1973, this earth dam stands at a height of 26 feet, with a hydraulic height of 24 feet and a structural height of 28 feet. It serves multiple purposes, including flood risk reduction, with a storage capacity of 147 acre-feet and a drainage area of 0.8 square miles.
This dam on the TR N FK BIG NEMAHA RIVER spans 570 feet in length and covers a surface area of 8 acres. Despite its low hazard potential, Upper Big Nemaha J-12a undergoes regular inspections every five years and was last assessed as being in satisfactory condition in April 2018. The dam has a normal storage capacity of 29 acre-feet and a maximum discharge rate of 787 cubic feet per second, providing essential water management for the surrounding area.
Owned by the local government, Upper Big Nemaha J-12a is an essential component of water resource management in the region. With its solid stone core and soil foundation, this dam ensures effective flood control and water storage capabilities, contributing to the overall resilience of the local water infrastructure. Its strategic location, efficient design, and regular maintenance make it a crucial asset for safeguarding against water-related risks and enhancing climate resilience in the area.
Year Completed |
1973 |
Dam Length |
570 |
Dam Height |
26 |
River Or Stream |
TR N FK BIG NEMAHA RIVER |
Primary Dam Type |
Earth |
Surface Area |
8 |
Hydraulic Height |
24 |
Drainage Area |
0.8 |
Nid Storage |
147 |
Structural Height |
28 |
Hazard Potential |
Low |
Foundations |
Soil |
Nid Height |
28 |
Seasonal Comparison
Weather Forecast
Nearby Streamflow Levels
Dam Data Reference
Condition Assessment
SatisfactoryNo existing or potential dam safety deficiencies are recognized. Acceptable performance is expected under all loading conditions (static, hydrologic, seismic) in accordance with the minimum applicable state or federal regulatory criteria or tolerable risk guidelines.
Fair
No existing dam safety deficiencies are recognized for normal operating conditions. Rare or extreme hydrologic and/or seismic events may result in a dam safety deficiency. Risk may be in the range to take further action. Note: Rare or extreme event is defined by the regulatory agency based on their minimum
Poor A dam safety deficiency is recognized for normal operating conditions which may realistically occur. Remedial action is necessary. POOR may also be used when uncertainties exist as to critical analysis parameters which identify a potential dam safety deficiency. Investigations and studies are necessary.
Unsatisfactory
A dam safety deficiency is recognized that requires immediate or emergency remedial action for problem resolution.
Not Rated
The dam has not been inspected, is not under state or federal jurisdiction, or has been inspected but, for whatever reason, has not been rated.
Not Available
Dams for which the condition assessment is restricted to approved government users.
Hazard Potential Classification
HighDams assigned the high hazard potential classification are those where failure or mis-operation will probably cause loss of human life.
Significant
Dams assigned the significant hazard potential classification are those dams where failure or mis-operation results in no probable loss of human life but can cause economic loss, environment damage, disruption of lifeline facilities, or impact other concerns. Significant hazard potential classification dams are often located in predominantly rural or agricultural areas but could be in areas with population and significant infrastructure.
Low
Dams assigned the low hazard potential classification are those where failure or mis-operation results in no probable loss of human life and low economic and/or environmental losses. Losses are principally limited to the owner's property.
Undetermined
Dams for which a downstream hazard potential has not been designated or is not provided.
Not Available
Dams for which the downstream hazard potential is restricted to approved government users.
Upper Big Nemaha J-12a